Pressure-sensitive hot-melt adhesives

ABSTRACT

A PRESSURE-SENSITIVE ADHESIVE COMPOSITION HAVING INSTANT ROOM TEMPERATURE TACK, GOOD COLD FLOW RESISTANCE AND GOOD SHEAR STRENGTH WHICH COMPRISES AS A FIRST COMPONENT A RESINOUS ATACTIC POLYPROPYLENE, AS A SECOND COMPONENT A RESINOUS RUBBERY BLOCK COPOLYMER OF STYRENE AND BUTADIENE OR ISOPRENE, AND AS A THIRD COMPONENT A MODIFIED OR UNMODIFIED ROSIN, A COUMARONE-INDENE RESIN, A POLYTERPENE RESIN, A DIENE-OLEFIN ALIPHATIC HYDROCARBON RESIN OR A POLYSTYRENE RESIN.

United States Patent 3,686,107 PRESSURE-SENSITIVE HGT-MELT ADHESIVESThomas E. Russell, Verona, N.J., assignor to The Flintkote Company,White Plains, N.Y.

No Drawing. Continuation of abandoned application Ser. No. 739,640, June25, 1968. This application Mar. 24, 1971, Ser. No. 127,794

Int. Cl. C09j 3/26 U.S. Cl. 260-27 BB 10 Claims ABSTRACT OF THEDISCLOSURE This application is a continuation of co-pending applicationSer. No. 739,640 filed June 25, 1968, now abandoned.

This invention relates to pressure-sensitive adhesives, and moreparticularly to pressure-sensitive adhesives that have instant roomtemperature tack, good cold flow resistance and shear strength, areessentially unaffected by moisture, and can be made as hot melts withoutsolvents.

Countless uses exist for pressure-sensitive adhesives that have goodquick tack at ordinary temperatures, adhere to numerous surfaces uponcontact with essentially no pressure, are essentially free of cold flow,so-called creep, resist shearing stresses, do not deteriorate undermoist conditions and retain their desirable properties during prolongedperiods of storage, i.e., have good shelf-life. Such uses include beingthinly coated onto the under surfaces of floor tiles and wall tiles thatthereafter can be set quickly and permanently on floors or walls. Thepressure-sensitive adhesives of this invention are especially suited forsuch uses, inter alia. Thus they can be coated onto substrates likefloor and wall tiles by the manufacturer, and covered with a removableprotective sheet to form a socalled peel-and-stick product.

An object of this invention is to provide pressure-sensitive adhesives.Another object of this invention is to provide pressure-sensitiveadhesives that have good instant tack, high strength in shear, virtuallyno cold flow, resistance to moisture and storage stability. A furtherobject of this invention is to provide a method for making suchpressure-sensitive adhesives by hot-melt means without solvents. Theseand other objects of this invention will be in part discussed in and inpart apparent from the following more detailed disclosure.

Broadly the pressure-sensitive adhesives of this invention contain threeresinous components which, in intimate combination with one another inthe proportions specified, provide the desirable properties hereinbeforediscussed. The primary components are a resinous rubbery block copolymerof styrene and butadiene or styrene and isoprene, an atacticpolypropylene polymeric resin, and one or more of a modified orunmodified rosin, coumarone-indene resin, polyterpene resin,diene-olefin aliphatic hydrocarbon resin or polystyrene resin. Otheringredients can, of course, be included in the adhesives to attainadditional desiderata, for example, an antioxidant to protect thevarious resins, especially during hot-melt blending and coating of theadhesive in molten condition onto substrates. Moreover, by selection ofparticular components from among the variety of each available, theproperties of the adhesive compositions can be modified somewhat asmight be necessary. For example, shear strength and hot and cold flowfor application can be modified by the selection as well as theproportioning of the rubbery block copolymer, whereas quick tack andpressure-sensitivity can be varied by the choice and proportion of theatactic polypropylene.

Rubbery block copolymers of styrene and butadiene or styrene andisoprene that are especially advantageous to use in the instantadhesives are those in which the monomers are not randomly mixed butrather are in groups of poly-monomers, i.e., groups or blocks ofpolystyrenepolybutadiene-polystyrene orpolystyrene-polyisoprenepolystyrene. The polystyrene groups havemolecular weights of from about 5,000 to about 125,000, preferablybetween about 8,000 and 45,000; the polybutadiene or polyisoprene blockshave molecular weights of between about 15,000 and about 250,000,preferably from about 35,000 to about 150,000. Such copolymers cancontain from about 20% to about of either block polymer. Such rubberyblock copolymers are commercially available under its trade name Kraton,for example, Kraton 101 and 102 which arepolystyrene-polybutadiene-polystyrene (S-BS) copolymers, and Kraton 107which is the polyisoprene (S-B-S) counterpart. They can be used inamounts of between about 7% and about 30% by weight of the tri-componentadhesive, preferably from about 10% to 25% by weight. Combinations ofdifferent rubbery block copolymers can be used.

Another principal component of the pressure-sensitive adhesivecompositions of this invention is an atactic polypropylene, anessentially non-crystalline polypropylene formed in comparatively smallamounts during the production of isotactic, or crystalline,polypropylene by stereoscopic polymerization of propylene. The solidatactic polypropylene has a molecular weight of between about 15,000 andabout 60,000, and preferably for suitability in the instant adhesivesfrom about 16,000 to about 20,- 000. A commercially available atacticpolypropylene for such use is available from Avisun Corporation underthe name Oletac 100. This component is included in the adhesivecompositions in an amount of from about 5% to about 35% by weightthereof, desirably in an amount between about 9% to about 30%.

The third principal component of the subject adhesives can be a modifiedor unmodified rosin, polyterpene, coumarone-indene, polystyrene ordiene-olefin aliphatic hydrocarbon resin. Such rosins include ethyleneglycol, polyethylene glycol, glycerol and pentaerythritol rosin esters,hydrogenated rosin esters or methylated rosin esters, for example, thecommercially available'materials Staybelite Ester 3 triethylene glycolester of hydrogenated rosin, Foral and highly stabilized ester resins ofpentaerythritol and rosin base, Hercolyn D hydrogenated methyl ester ofrosin purified by steam distillation, and Pentalyn H pentaerythritolester of hydrogenated rosin. Suitable terpene polymers are, for example,solid or liquid poly-(a-pinene) such as Piccolyte Alpha 10, 25 andhaving corresponding softening points and degrees C. and molecularWeights of 100, and 1200, and poly-(fi-pinene) such as Piccolyte S-l00and S-ll5 having molecular weights of about 1200. Coumarone-indeneresins are available as Piccovar L-30 and L-60, which have molecularweights of about 600 to 700, Nevex 100 and Nevchem 100 and 140.Diene-olefin aliphatic hydrocarbon resins are, for example, Piccopale45, 85 and 110, which have molecular weights of about 600, 1000 and1500. The polystyrene resins are of intermediate molecular weight, e.g.,from about 300 to about 6000, preferably to about 1000. Suitablecommercially available resins include Piccolastic A, D and E series,especially the A series.

These third-component resins can be used in the adhesives in an amountof from about 45% to about 80% by weight of the principal components,preferably between about 50% and about 65%. They can be used incombination either with resins of the same class, for example, thePiccolyte Alpha 25, 100 and 115, poly-(otpinene) resins or two or threeof the different classes, for example Foral 105 highly stabilized esterresin and Piccolyte Alpha 25. In general the proportions of each resinin a class, or of each resin of the different classes, can vary quitewidely, the determining factor seeming to be those discussedhereinbefore, e.g., the specific desired extent of properties such asquick tack, pressure-sensitivity, cold flow, shear strength, coatabilityof the molten adhesive and so forth. No specific rule presently appearsto prevail. As an example, a highlysatisfactory and therefore apreferred combination is from about to about 40% by weight of themodified or unmodified rosin component and between about and about 50%by weight of the polyterpene, their total being about 50% to about 65%of the tri component composition.

From about 0.01% to about 2.0% by weight of one or more antioxidantsdesirably are added to the adhesives. Antioxidants known to be effectivefor the various components, especially for the rubbery block copolymerand the atactic polypropylene, can be used. Such antioxidants include,for example, Ionox 220 and 330 tris (di-t-butyl-p-hydroxybenzy-trimethylbenzene, Dalpac 4C 2,6-di(t-butyl)-p-cresol, Naugawhitealkylated bisphenol and Butyl Zimate" zinc dibutyl dithiocarbarnate.Ordinarily about 0.4% to about 1.0% of antioxidant, based on the amountof composition, is sufiicient.

The rubbery polystyrene-poly(conjugated diene)-polystyrene blockcopolymers are thermoplastic in nature and have no sharp melt point.Thus they cannot simply be melted with the other resins to anyappreciably significant extent. For example, Kraton 107 can be hotmelted with the other components to an extent of perhaps up to about10%, although not easily beyond about 5%. Kraton 101 and 102, however,are far less addable by melting. It has been found possible, however, toavoid using a solvent for the rubbery copolymer, and instead to preparethe pressure-sensitive adhesives of this invention containing sufiicientrubbery block copolymers by a completely hot-melt technique. Anadditional benefit of the method is that the adhesives can be meltcoated onto suitable substrates; solvent coating systems areunnecessary.

Initially at least a substantial portion of a rubbery block copolymer,which is ordinarily produced in crumb form, is mechanically mixed with aportion of the rosin, polyterpene, coumarone-indene, diene-olefin orpolystyrene component to form an intimate, meltable mix. Generally thelatter component is preblended in an amount ranging from about one-halfto about equal the amount of block copolymer, preferably at least aboutthree-quarters as much. Considerable variation is possible dependingupon the specific resins and overall proportions. Mastication of thosetwo components can be accomplished in an ordinary rubber mill or otherhigh shear kneading or milling device, for example, a Banbury mill.Pre-blending is at room temperature or up to about 150 F. Although it ispossible to work at either lower or higher temperatures, practicalfactors tend to preclude doing so, for example, degradation of theresins and difficulty of blending and removing them. Preblending in arubber mill at room temperature ordinarily requires in the order ofabout one-half hour to about three hours, usually about one hour, toprepare a uniform mix of rubbery, crepe-like consistency. The meltablepreblend thus prepared can be diced or sliced for convenient subsequentmelting.

The adhesive composition is completed by melting the preblendedcomponents in an agitated vessel heated at from about 270 F. to about400 F usually about 325 to 375 F. An antioxidant can be added as soon asit readily will mix with the melting preblend. Thereafter the othercomponents of the adhesive are added directly to the hot melt,preferably first any of the polyisopreneblock copolymer that was notpreblended followed by the atactic polypropylene and then the remainingmodified or unmodified rosin, polyterpene, coumarone-indene,diene-olefin or polystyrene resin component. The batch is blended untila clear, smooth-running, homogeneous composition is formed. Thecomposition can be coated onto a substrate, for example, as a coatingfrom about 1 to about 5 mils thick, preferably about 2 to 4 mils, or canbe cooled to a resilient, tacky solid at room tem-, perature forsubsequent remelting and application, e.g., at about 350 F.

Adhesives according to this invention, which are at least essentiallysolids, have a Brookfield viscosity (No. 7 spindle at 300 F., 20 r.p.m.)in the range of about 25,000 to 150,000 cps., preferably about 35,000 to65,000 cps.; a softening point (Ring and Ball, ASTM D-3626) of at leastabout 200 F., preferably from about 225 F. to 275 F.; a penetrationhardness (ASTM D-5-49, room temperature) in the range of about 0.35 cm.to 1.3 cm., preferably about 0.5 cm. to 0.8 cm.; and a loss on heating(ASTM D6-39T, 5 hours at 300 F.) of about 10% maximum, preferably belowabout 5%.

The following examples are specific embodiments of adhesive compositionsset forth to illustrate the invention.

EXAMPLE 1 A mix of 15.00 parts (by weight unless otherwise specified) ofKraton 101 polyestyrene-polybutadiene-polystyrene block copolymer crumband 11.00 parts of Foral 105 stabilized pentaerythritol rosin ester wasmasticated in a rubber mill for about one hour at room temperature untila uniform crepe-like composition was formed. The composition was thenmelted at about 325 F. to 350 F. in a heated vessel having a stirrer. Anantioxidant, 0.50 part of Dalpac 4C, a 2,6-di(t-butyl)-p-cresol, wasadded as the preblend melted. Thereafter 7.00 parts of Kraton 107polystyrene-polyisoprene-polystyrene resin, 18.00 parts of Oletac 100atactic polypropylene, 12.00 parts of Piccolyte Alpha and 36.50 parts ofPiccolyte Alpha 25, both polyterpene resins were added to the hot melt.Mixing of the hot melt was continued for about one-half hour until aclear, smoothly-flowing, homogeneous composition was formed. Thecomposition was poured into a mold and cooled to a resilient block atroom temperature.

A portion of the solid adhesive thus prepared was melted and coated atabout 300 F. onto 9" x 9" vinylasbestos floor tiles. Thepressure-sensitive coating, which was about 4 mils thick on the tiles,had good quick tack, good pressure-sensitivity and virtually no coldflow. Some of the tiles were placed on a cleaned concrete floor on whichthey had excellent shear strength. Similar results were obtained withother tiles placed on a vertical plywood wall.

The adhesive composition was coated onto various materials and testedfor peel strength (Pressure Sensitive Tape Council #1, at 180 F.). Theresults were greater than 160 ounces per inch on plywood, stainlesssteel, asbestos cement and vinyl asbestos substrates. The results wereessentially the same both after 4 months under water and afteraccelerated shell life at F. The alkaline nature of moist cement did notaffect the adhesion. Silicon-treated parchment paper was placed on theadhesive coating during storage, and could be peeled off easily for use.

A coating 2 mils thick vinyl-asbestos tile produced a shear adhesion, orholding power, at 130 F. (P.S.T.C. #7) of about 30 minutes.

EXAMPLE 3 A pressure-sensitive hot-melt adhesive was preparedsubstantially as described in Example 1 from a preblend of 7.60 parts ofKraton 101 and 7.60 parts of Foral 105, to which preblend were added4.50 parts of Kraton 107, 27.70 parts of Oletac 100, 31.80 parts ofForal 105, 17.20 and 3.10 parts of Piccolyte Alpha 25 and 10,respectively, and 0.5 part of Dalpac 4C antioxidant. Coatings of theadhesive on various materials produced similar satisfactory results asdescribed in Example 1.

EXAMPLE 4 A pressure-sensitive hot-melt adhesive was preparedsubstantially as described in Example 1 from 15.10 parts of Kraton 101and 15.10 parts of Nevchem 140 coumarone-indene resin, to which preblendwere added 9.75 parts of Oletac 100, 10.70 parts of Ne vchem 140, 48.75parts of Cumar MH 2 /2 coumarone-indene resin and 0.60 part of Dalpac 4Cantioxidant. Coatings of the adhesive on various materials producedsimilar satisfactory results as described in Example 1.

EXAMPLE 5 A pressure-sensitive hot melt adhesive was preparedsubstantially as described in Example 1 from a preblend of 10.00 partsof Kraton 107 and 10.00 parts of Foral 105, to which preblend were added30.00 parts of Oletac 100, 20.00 parts of Foral 105, 29.00 parts ofPiccolyte Alpha 25 and 1.00 part of Dalpac 4C antioxidant. Coatings ofthe adhesive on various materials produced similar satisfactory resultsas described in Example 1.

EXAMPLE 6 A pressure-sensitive hot-melt adhesive was preparedsubstantially as described in Example 1 from a preblend of 20.75 partsof Kraton 101 and 20.75 parts of Foral 105, to which preblend were added4.45 parts of Kraton 107, 14.83 parts of Oletac 100, 14.95 parts ofForal 105, 23.30 parts of Piccolyte Alpha 25 and 0.97 part of Dalpac 4Cantioxidant. Coatings of the adhesive on various materials producedsimilar satisfactory results as described in Example 1.

EXAMPLE 7 A pressure-sensitive hot-melt adhesive was preparedsubstantially as described in Example 1 from a preblend of 15.0 parts ofKraton 101 and 11.00 parts of Foral 105, to which preblend were added5.0 parts of Kraton 107, 20.00 parts of Oletac 100, 23.5 parts of Foral105, 25.0 parts of Stabelite 3 triethylene glycol ester of hydrogenatedrosin and 0.5 part of Dalpac 4C antioxidant. Coatings of the adhesive onvarious materials produced similar satisfactory results as described inExample 1.

EXAMPLE 8 A pressure-sensitive hot-melt adhesive was preparedsubstantially as described in Example 1 from a preblend of 24.00 partsof Kraton 102, 9.25 and 6.95 parts of Piccolyte Alpha 115 and 110,respectively, to which preblend were added 16.65 parts of Oletac 100,42.55 parts of Piccolyte Alpha 25 and 0.6 part of Dalpac 4C antioxidant.Coatings of the adhesive on various materials produced similarsatisfactory results as described in Example 1.

It will of course be understood that numerous modifications can be madein the ingredients, proportions and conditions described in theforegoing examples without departing from the scope of this invention asdisclosed hereinbefore and as defined in the claims appended hereafter.

I claim:

1. A pressure-sensitive adhesive composition having in stant romtemperature tack, good cold flow resistance and good shear strengthwhich consists essentially of: as a first component, from about 5% toabout 35% of an atactic polypropylene having a molecular weight in therange of about 15,000 to about 60,000; as a second component, from about7% to about 30% of a polystyrenepolybutadiene-polystyrene or apolystyrene-polyisoprenepolystyrene block copolymer whose polystyreneblocks have molecular weights of from about 5000 to about 125,000 andare from about 20% to about by weight of said copolymer, and whosepolybutadiene or polyisoprene blocks have molecular weights of fromabout 15,000 to about 250,000; and as a third component, from about 45%to about 80% of an ethylene glycol, polyethylene glycol, glycerol orpentaerythritol rosin ester, hydrogenated rosin ester or methylatedrosin ester, a conmarone-indene resin having a molecular weight of aboutto about 800, a poly-(u-pinene) or poly-(B-pinene) resin, a diene-olefinaliphatic hydrocarbon resin having a molecular weight of about 500 toabout 1800, or a homopolymeric polystyrene resin having a molecularweight of about 200 to about 6000; said percentages being based on thetotal weight of said components in said adhesive composition.

2. A pressure-sensitive adhesive composition according to claim 1containing from about 9% to about 30% of said first component, fromabout 10% to about 25% of said second component, and from about 50% toabout 65% of said third component.

3. A pressure-sensitive adhesive composition according to claim 1wherein said atactic polypropylene first component has a molecularweight of from about 16,000 to about 20,000.

4. A pressure-sensitive adhesive composition according to claim 1wherein said. polystyrene blocks have molecular weights of from about8000 to about 45,000 and said polybutadiene or polyisoprene blocks havemolecular weights of from about 35,000 to about 150,000.

5. A method of making a pressure-sensitive adhesive composition havinginstant room temperature tack, good cold flow resistance and good shearstrength which comprises: masticating together as a first component fromabout 7% to about 30% of a polystyrene-polybutadienepolystyrene or apolystyrene-polyisoprene-polystyrene block copolymer whose polystyreneblocks have molecular weights of from about 5000 to about 125,000 andare from about 20% to about 80% by weight of said copolymer, and whosepolybutadiene or polyisoprene blocks have molecular weights of fromabout 15,000 to about 250,000, and as a second component from about 45%to about 80% of an ethylene glycol, polyethylene glycol, glycerol orpcntaerythritol rosin ester, hydrogenated rosin ester or methylatedrosin ester, a coumaroneindene resin having a molecular weight of fromabout 150 to about 800, a poly-(a-pinene) or poly(B-pinene) resin, adiene-olefin aliphatic hydrocarbon resin having a molecular weight ofabout 500 to about 1800, or a homopolymeric polystyrene resin having amolecular weight of from about 200 to about 6000, to form a uniformpreblend thereof; melting said preblend to form a hot-melt mix; andblending into said hot-melt mix as a third component from about 5% toabout 35 of an atactic polypropylene having a molecular weight of about15,000 to about 60,000 to form a homogeneous adhesive composition; saidpercent values being by weight of the adhesive composition.

6. A method of making a pressure-sensitive adhesive compositionaccording to claim 5 wherein said preblend is formed at a temperature offrom about 60 F. to about 150 F., and said homogeneous adhesive isblended at a temperature of from about 270 F. to about 400 F.

7. A method of making a pressure-sensitive adhesive compositionaccording to claim wherein said first component is used in an amount offrom about to about said second component is used in an amount of fromabout to about and said third component is used in an amount of about 9%to about 30%.

8. A method of making a pressure-sensitive adhesive compositionaccording to claim 5 wherein the amount of said second componentpreblended with said first component is from about one-half to aboutequal the amount of said first component, and which further comprisesblending the remaining portion of said second component into saidhot-melt of said preblend.

9. A method of making a pressure-sensitive adhesive compositionaccording to claim 5 wherein said atactic polypropylene third componenthas a molecular weight of from about 16,000 to about 20,000.

References Cited UNITED STATES PATENTS 3,239,478 3/1966 Harlan 260273,360,488 12/1967 Hall et a1 260-23 DONALD E. CZAJA, Primary Examiner W.E. PARKER, Assistant Examiner U.S. Cl. X.R.

Patent No. 3 686 '107 Dated August 22,. 1972 Inventor(s) Thomas RussellIt is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Col. 2, line 21, change "its" to "the line 24,; change "S-B-S" to S -I-Sline 59, change first "and" to in Col. 3, line 6, delete last comma,line 7, after "resins" insert comma; Col. 4, line 45, after "resins"insert comma; C01. 6, line 6, change "rom" to room Signed and sealedthis 23rd day of January 1973.

(SEAL) Attest! I EDWARD M.,FLETCHER,JR. ROBERT SOTTSCHALK AttestingOfficer Commissioner of Patents FORM FO-1050 (10-69) USCOMM-DC 50376-P59U.$ GOVERNMENT PRINTING OFFICE Hi9 0-366-334

